With the growing demand of batteries as an energy source, the interest in rechargeable electrochemical devices is increasing, and in particular, there is a further increase in the demand for and interest in lithium secondary batteries.
A lithium secondary battery includes an electrode assembly composed of a cathode, a separator, and an anode. The separator may be manufactured by coating a porous polymer substrate with a slurry including inorganic particles and an organic binder polymer, followed by drying, and the cathode and the anode are manufactured by applying, to an electrode current collector, a slurry for an electrode compound including inorganic particles serving as an active material and an organic binder polymer. The slurry includes the inorganic particles with the aim to intercalcate/deintercalate a lithium ion or improve ionic conductivity of an electrolyte solution, but the inorganic particles tend to sink over time. Accordingly, when the inorganic particles are not dispersed in the slurry uniformly or sink due to low dispersion stability, condensation or sediment occurs after the slurry is applied to the porous polymer substrate or the electrode current collector (hereinafter, collectively referred to as a ‘substrate’). As a result, an adhesive strength between the inorganic particles in the slurry and the substrate reduces, and as charging and discharging of the battery proceeds, separation between the inorganic particles or between the inorganic particles and the substrate occurs, and consequently, the inorganic particles do not fulfill their function.
To solve the problem, studies have been conducted to improve dispersibility of inorganic particles, for example, a technology that uses a surfactant as a dispersant when dispersing an active material and carbon black in a solvent. However, because adsorption of a surfactant on the particle surface is low, a large amount of surfactants is required to achieve good dispersion stability. As a result, an amount of inorganic particles that can be included in a slurry relatively reduces, and consequently, inorganic particles do not tend to fulfill their intrinsic function. Also, if adsorption of a surfactant on particles is insufficient, inorganic particles are prone to agglomeration. Also, a general surfactant has a remarkably low dispersion effect in an organic solvent, compared to dispersion in a water-soluble solution.